1. Field of the Invention
The present invention relates to broad bandwidth planar power combiner/divider device.
2. Description of the Related Art
FIG. 1 of the accompanying drawing illustrates a power combiner/divider device 10 as described by W. Yau and J. M. Schellenberg in an article entitled "An N-Way Broadband Planar Power Combiner/Divider" published by Microwave Journal, Vol. 29, No. 11 November 1986, pages 147 to 151 (See also U.S. Pat. No. 4,835,496 issued May 30, 1989). The device 10 utilizes the Dolph-Chebyshev tapered transmission line and comprises a five-way power combiner/divider for operating between 2 and 18 GHz. The device comprises a quartz substrate on which are provided five tapering conductors 1 to 5 which merge into one central conductor 12 substantially at a junction 14 with the central conductor. The gap spacings between adjacent conductors 1 to 5 are identical and are relatively small (0.038 mm) to ensure that the coupled structure conformed to the Dolph-Chebyshev tapered line condition. An isolation network formed of chip resistors R connects between the tapering conductors 1 to 5 and help to give a broadband performance. This type of combiner/divider device provides an impedance transformation of N times 50 ohms distributed ports to one 50 ohm central port Choosing the Dolph-Chebyshev taper has the feature that it has minimum reflection coefficient magnitude in the passband for the specified length of taper or conversely for a specified maximum magnitude reflection coefficient in the passband, the Dolph-Chebyshev taper has a minimum length. The contour and the length of the taper determine the in-band reflection coefficient and the lower cut-off frequency, respectively.
This known design of planar power combiner/divider can have a number of drawbacks. One of these is that the device can have a distinct resonance frequency caused by the transverse resonance mode supported by the cross-section of the tapered transmission line. Another of these drawbacks can be that the chip resistors R are difficult to connect to the conductors 1 to 5 and also they generally do not give their anticipated performance due to inductive and capacitive parasitic effects.